Output structure for electron discharge devices employing cavity resonators



1950 P. w. CRAPUCHETTES 2,947,908

OUTPUT STRUCTURE FOR ELECTRON DISCHARGE DEVICES EMPLOYING CAVITY RESONATORS Original Filed May 6, 1955 2 Sheets-Sheet 1 1960 P. w. CRAPUCHETTES 2,947,908

OUTPUT STRUCTURE FOR ELECTRON DISCHARGE DEVICES EMPLOYING CAVITY REISGNATORS Original Filed May 6, 1955 2 Sheets-Sheet 2 Mal CQQFUCHETIES',

IN V EN TOR.

2,947,908 a OUTPUT STRUCTURE non ELECTRON ms- CI -IARGE DEVICES ENIPLOYING CAVITY RESONATORS Paul W. Crapuchettes, Atherton, Calif., assignor to Litton Industries of California, BeverlyHills, Calif.

Continuation of application Ser. No. 506,650, May 6, 1955. This application Apr. 15, 1958, Ser. No. 728,748

' 11 Claims. (Cl. 3155.46)

' This invention relates to an output structure for electron discharge devices employing cavity resonators, and more particularlyto a velocity modulated vacuum tube output structure wherein an output cavity is symmetrically coupled to an output waveguide through the end of the cavity. Although the. invention is applicable in general to all forms of high frequency tubes which employ torroidal resonators, for purposes of simplicity it will be disclosed with particular reference to klystrons. This application is a continuation of my copending US. patent application Serial No. 506,650, filed May 6, 1955, now

the cavity at a region where the magnetic field is high.

According to the other prior art technique, energy is extracted from the output cavity through an iris machined in the side of the output cavity. When iris coupling is employed, the output structure-may, for example, comprise a pair of exponential ramps positioned adjacent the iris in the side of the output cavity, these ramps serving as an impedance transformer for coupling energy from the cavity to an associated output waveguide.

Although each of the above techniques for extracting energy from high frequency vacuum tubes has been widely used, as for example, in both reflex and multicavity klystrons, they inherently limit the operation of the tubes in which they are utilized in several manners. Firstly, although the mutual coupling between the various regions of the output cavity of a klystron is usually considered to be relatively good, the extraction of energy from one particular region in the side of the cavity does nevertheless preclude hightly eflicient operation. More particularly, when energy is extracted from one localized region of the output cavity, it is clear that almost all of the energy stored in this region of the cavity is delivered to the output system. Although theoretically it would appear that this energy is immediately replaced by redistribution of energy from the remainder of the cavity owing to mutual coupling, there is substantial evidence that a completely uniform redistribution of energy does not occur, particularly where the output aperture in the side of the cavity covers an appreciable portion of the cavity periphery, as in high power klystrons. Consequently, a

depression exists in the field in the output cavity adjacentthe output structure, and the maximum power output derived from the cavity is less than what would be anticipated; accordingly, the efiiciency of the klystron is lower than the efficiency expected for a given power input and cavity structure.

Still another basic disadvantage of the output coupling structures of the prior art is encountered when it is Un w S a s Pat- 50 desired, to inductively tune a multicavity klystron. o n to the fact that the field in the output cavity-1s not com pletely symmetrical, it is often-difficult to gang the tuning conrols for several cavities particularly when the tuning elements are annular members concentrically positioned within the cavities. A still further disadvantage of the prior art output structures is that it is diflicult to place an electron beam controlling magnet or electromagnet adjacent the output cavity owing. to the fact that these output structures normally protrude from the side of the cavity.

The present invention, on-theother hand, provides an output structure for velocity modulated tubes which obviates the above and otherdisadvantages of the output structures of the prior. art, According to the basic concept of the invention, energy is extracted from an output cavity through an annular 'opening at the end of the output cavity, the annular. openingbeing formed by the end of the 'cavityand the electron beam channeling tubewhich extends intothecavity at that end. More specifically, one at the electronbeam channeling tubes extending into the .outputcavity is utilized as the central conductor of a coaxial line having asits outer conductor the adjacent wall of the output cavity, and energy is extracted by joining the end of the output cavity to a rectangular waveguide, the beam-channeling tube being operative as a transition post mounted in the waveguide to provide a coaxial line-to-wziveguide transition.

According to theinvention, the novel output structure herein disclosed is especially applicable to high power multicavity klystrons although it may also be utilized with a single cavity tube such as a reflex klystron, for example. Depending upon the type of tube in which the invention is utilized, the tubular member employed may be either a drift tube, the collector tube or a portion of the electron gun. In addition, various forms of impedance transforming element may be utilized within the outputwa-veguide to providea broad band and substantially'non-reflective coaxial line-to-waveguide transition, thereby enabling relatively large amounts'of power to be extracted from the klystron over a relatively large frequency range. I p

Owing to the fact that a completely symmetrical field is produced in the output cavity through the utilization of the invention herein disclosed, increased efiiciency and practicalinductive tuning may be readily-achieved. In addition, the output cavity may be readily constructed so that its tuning curve conforms to the tuning curves of the other cavities of a multicavity klystron, thereby permit ting gauging of the tuning controls of all cavities of the tube. A still further advantageous feature of'the invention isthat the lateral peripheryof the output cavity includes. no output structure, thereby permitting theme of a. continuous magnet assembly from the electron gun on past the output cavity for controllingthe cross sectional area of the electron beam.

. It is therefore an object of the invention to provide klystrons inwhich the field within the output cavity is symmetrical. I

Another object of the invention is to provide multicavity klystrons in which the tuning'curves of the several cavities are substantially the same,'thereby permitting the tuning controls to be ganged. I

,Still anotherobject of the invention is to providea klystron output structure wherein the output signal is extracted through an annular opening in one end of the output cavity. a i a A further object of the invention is to provide klystrons wherein one end of the output cavity and the beam channeling tube which enters therein are employed as a coaxial link .bet-Wen the cavity and an associated rectangular output waveguide.

A still further object of the invention is to provide klystrons in which an output signal is extracted through a symmetrical coaxial link in one end of the output cavity, the beam channeling tube which extends into the cavity at that end functioning as the inner conductor of the coaxial link and as a transition post in an associated rectangular output waveguide.

An additional object of the invention is to provide klystrons in which the output structure is symmetrically connected to one end of the output cavity, the lateral periphery of the output cavity being continuous. and uniform The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Fig. 1 is an oblique view, partly in section, of a portion of a multicavity klystron which includes one embodiment of the output structure of the invention;

Fig. 2 is an oblique view, partly in section, of a portion of a reflex klystron employing the novel output structure of the invention; and

Figs. 3 and 4 are schematic views, partly in section, of multicavity klystrons which include modified forms of the output structure of the invention.

Referring now to the drawings, wherein like or corresponding parts are designated by the same reference characters throughout the several views, there is shown in Fig. 1 a multicavity klystron which utilizes the novel output structure of the invention. Basically the klystron shown in Fig. 1 includes an electron gun 10, only a portion of which is shown, an input or buncher cavity 12 connected to the electron gun, an output cavity 14 coupled to input cavity 12 by a drift tube 16, and a collector assembly, generally 20, which is interconnected with output cavity 14 by the novel output structure of the invention, which is generally designated 22.

In operation the klystron functions in the manner Well known to the art to produce an amplified signal in output cavity 14. Briefly stated, electron gun is operable to project an electron beam through input cavity 12, drift tube 16, output cavity 14 and into collector 20, the electrons in the beam being velocity modulated as they pass through the input cavity by an electrical input signal applied to an input waveguide 23 which terminates within the input cavity. The velocity modulated electrons are thus bunched in the well known manner as they pass through drift tube 16, and function to deliver energy to the output cavity as they pass through the gap between the drift tube and a collector tube 24 which forms a portion of collector assembly 20. The electrons thereafter continue on through collector tube 24 into the main body of the collector assembly, where they are collected or absorbed. The collector assembly may also include a suitable cooling mechanism, such as a water jacket, for example, for removing heat generated by the absorption ofthe electrons in the electron beam.

Referring now with particularity to the novel output structure of the invention, the klystron shown in Fig. 1 includes a rectangular output waveguide 26 through which collector tube 24 extends, the upper side of the waveguide, as viewed in the drawing, being brazed or otherwise affixed to the collector tube. The lower side of the waveguide, on the other hand, is apertured and joined to the upper end of output cavity 14 to provide an opening through which collector tube 24 extends into the output cavity, the collector tube being spaced radially from the sides of the junction between the output cavity and the waveguide. Accordingly, the collector tube functions in cooperation with the adjacent junction to provide a coaxial link between output cavity 14 and output waveguide 26 for transmitting to the output waveguide energy generated within the cavity, the collector tube also serving as a transition post to provide a coaxial line to rectangular waveguide transition.

As illustrated in Fig. 1 waveguide 26 also includes an output window 28 which is substantially transparent to microwave energy and which is hermetically sealed to the metallic body of the waveguide. In addition, the output waveguide may also include an impedance matching device such as a flexible diaphragm 30 afiixed to the interior wall of the waveguide at an effective distance of A wavelength from tube 24, the diaphragm being selectively deformable upon rotation of an adjusting screw 32. It is clear, of course, that numerous other forms of matching devices, such as those employing a plunger actuated through a sylphon bellows, could be utilized in place of the specific structure shown.

The particular klystron shown in Fig. 1 also includes an inductive tuning system which may be utilized for either individually or gang tuning input cavity 12 and output cavity 14. The specific tuning system illustrated in the drawings is of the type disclosed in copending US. patent application Serial No. 418,303, filed March 24, 1954, for Cavity Resonator Electron Discharge Device, by Charles V. Litton, and includes an axially movable annular member, such as member 34, positioned within each cavity, each member being moved by movement of an associated mounting rod which extends through a hermetically sealed bellows unit. The mounting rods for the input and output cavities are designated in Fig. 1 by the reference numerals 36 and 38, respectively, while the bellows unit for the output cavity is designated 40. It will be recognized by those skilled in the art that numerous forms of mechanical devices, such as the one shown in the above'mentioned copending application, may be utilized for ganging rods 36 and 38 to provide simultaneous tuning of both input and output cavities. Inasmuch as the specific gang tuningstruoture of the tuning mechanism is not part of the invention, the gang tuning structure is merely shown schematically in Fig. l by the dotted line 41.

It should also be expressly pointed out that the klystron may also include a magnet or electromagnet assembly for controlling the path of the electron beam within the several beam channeling tubes of the klystron. Although for purposes of simplicity no magnetic circuit has been shown in Fig. 1, it will be recognized that should one be employed it may extend from adjacent the electron gun all the way to output waveguide 26 without interruption, whereas the magnetic circuits employed in the prior art must be split adjacent the output cavity in order to provide space for the klystron output structure. As a consequence of the above-mentioned feature of the invention, the cross sectional area of the electron beam may be accurately controlled without discontinuity all the way to the collector assembly, thereby preventing electrons in the beam from striking drift tube 16 and the lower portion of collector tube 24.

Referring once more to Fig. 1 and to the novel output structure therein shown, it should be noted that the distance between collector tube 24 and the adjacent juncture between the output cavity and waveguide is preferably relatively small since the annular aperture at the end of the cavity may be efiectively considered as a capacitance in series with the capacitance of the gap between the drift tube and collector. Considered from a different aspect, if the combination of collector tube 24 and the adjacent juncture is thought of as a coaxial transmission system terminated by the relatively low impedance of the output cavity, then it is clear that if the coaxial line is to have a relatively low characteristic impedance for matching the cavity, then the, ratio of the radii of the ant seouter and inner conductors of the coaxial line should be relatively close to unity.

It should also be pointed out that the length of collector tube 24 within output waveguide 26 and output cavity 14 is also a factor to be considered in constructing a klystron which includes the output structure of the invention. More particularly its length should be selected to avoid resonance at undesired frequencies with in or near the frequency spectrum over which the klystron is designed to operate.

Consider now the functioning of the output structure of the invention when the vacuum tube employing it is placed in operation. The velocity modulated electron :stream bunches in the conventional manner and delivers output energy to output cavity 14 as the electrons traverse the gap between drift tube 16 and collector tube 24, the output energy preferably exciting the output cavity in its dominant or TM mode. the output aperture in the cavity is concentric with the cavity itself, it will be recognized that the field pattern of the output cavity will be symmetrical about any transverse plane taken through the cavity.

As the output energy extracted from the electron stream excites the output cavity, the coaxial link between the output cavity and the output waveguide is also excited to propagate energy from cavity 14 into waveguide 26, collector tube 24 functioning as the inner conductor of the coaxial link and in addition as a conventional transi-' tion element for transforming the impedance of the wave- ;guide to the impedance looking back through the coaxial link into the cavity. Consequently, the energy received through the coaxial link undergoes a mode transition and is in turn propagated down waveguide 26 and through window 28 without setting up excessive reflections which would result in standing waves. It will be recognized by those skilled in the art that the maximum amount of reflection permissible is a variable factor and will be controlled in part by the circuit application of the klysiron and the degree of coupling desired between its (output cavity and the load.

Considering now the advantages provided through the utilization of the output structure of the invention, it will be recognized that the generation of a symmetrical field in the output cavity facilitates practical inductive tuning of the cavity whereas in the prior art klystrons accurate inductive tuning has been diflicult to achieve. In addition the generation of a symmetrical field in the output cavity permits gauging of the tuning controls for all the cavities of a multicavity klystron, even under heavy load conditions, a feat heretofore extremely difficult to accomplish. Still another important advantage provided by the output structure of the invention is an increase in klystron efliciency owing to the fact that energy is extracted from the entire cavity, andnot from a limited 'lateral area. As previously noted herein-above a still further advantage of the invention is that it permits the utilization of a contiguous magnetic field in high power klystrons, thereby preventing electron bombardment of the beam channeling tubes and avoiding the concomitant heating effects which ensue therefrom.

It is to be expressly understood, of course, that the output structure of the invention may also be employed in other forms of velocity modulated vacuum tubes, such as reflex klystrons, for example, and in addition may be modified in numerous particulars without departing from the basic concept herein set forth. With reference now to Fig. 2 there is shown a reflex klystron which incorporates the output structure ofthe invention, the klystron basically comprising an electron gun generally designated 40, a resonator cavity 42, a repeller assembly 'generally'designated 44, and an output waveguide 46.

J Electron gun 40 includes a cathode subassembly, diagrammatically indicated by the dotted lines '48, and 'a combination housing and beam channeling tube 50 only a portion of which is shown. As viewed in the draw- Owing to the fact that.

mg; the upper end of tube 50 is affixed to the lowerside of waveguide =46, and extends into cavity 42 but is spaced also includes a repeller 58 which is connected to a' conductor 59, the combination of the repeller and its associated conductor being insulatively interconnected to housing member 56 by a glass bead 60.

As shown in Fig. 2, the lower wall of cavity 42 is connected to waveguide 46 by a necked down region which is spaced from beam tube 50 to form therewith a coaxial link between the cavity and the output waveguide. It.

will be noted that beam tube 50 thus forms both the inner conductor of the coaxial link and a transition post to provide a coaxial line-to-rectangular waveguide transition. It will alsobe noted that the lower portion of beam tube 50 tapers outwardly to a relatively large diameter, the tapered region functioning as a blended doorknob transition of the type well known to the microwave art for matching a rectangular wave guide to a coaxial line.

In operation oscillations are built up in cavity 42 by the well known reflex klystron action wherein the incident electron beam' is repelled and bunched through the combined interaction of repeller 58 and the cavity resonator. The oscillatory output energy thus built up in the cavity is then transmitted through the coaxial link into the output waveguide where it is transformed and propagated through an associated output window.

It will be recognized, of course, that the reflex klys tron shown in Fig. 2 may be both inductively tuned in the manner previously described for the klystron shown in Fig. 1 and electronically tuned in the conventional manner through control of the repeller potential. It should also be clear that modifications may be made in the specific output structure shown Without departing from the spirit and scope of the invention. For example, in the reflex klystron shown in Fig. 2 the output waveguide could be located at the top of the resonator cavity with the repeller housing functioning as the inner conductor of the coaxial link and as the impedance matching element of the waveguide transition; obviously if the structure is thus modified tube 50 will then be affixed directly to the lower end of the cavity.

With reference now to Figs. 3 and 4, there are shown schematic views of portions of two multicavity klystrons wherein modified forms of the invention are employed. Referring with particularity to Fig. 3, there is shown a'klystron in which a cylindrical tube 60 extends between output cavity 14 and output waveguide 26 to provide a relatively long coaxial link between the cavity and waveguide. In addition, the transition between the coaxial line and output waveguide employs an extension tube 62 which terminates adjacent the collector. This particular form of transition is well known to the art as a crossed transition and is frequently employed where a relatively narrow band width is desired.

The klystron shown in Fig. 4, on the other hand, em ploys drift tube .16 as the inner conductor of the coaxial link, and in addition, is constructed with the lower end of the cavity affixed directly to the top of a ridged output waveguide 64. It will be recognized by those skilled in the art that the utilization of one or more ridges,

indicate that the basic concept of the invention is not restricted to a particular form of waveguide transition or to the use of the collector tube as the inner conductor of the coaxial link which couples to the output cavity. Inasmuch as numerous other modifications and alterations will occur to those skilled in the art, it is to be expressely understood that the invention is to be limited only by the spirit and scope of the appended claims.

What is claimed as new is:

1. In a tunable velocity modulated vacuum tube wherein high frequency electrical energy is generated by bunching the electrons in an electron stream, the combination comprising: a cavity resonator of substantially constant volume having a first and second apertured ends, said resonator having an axis extending through the center of the apertures in said first and second ends; a first electron beam channeling tube extending into said second end of said cavity resonator, said first tube being concentrically positioned with respect to said resonator and being connected thereto at said second end thereof: a rectangular waveguide having a pair of broad Walls and a pair of narrow walls and an axis of symmetry, said rectangular waveguide being positioned adjacent said first end of said resonator with said broad walls perpendicular to the axis of said resonator and said axis of said symmetry intersecting said resonator axis: a coaxial link intercoupling said resonator and said waveguide, said coaxial link including a hollow sleeve interconnecting said first end of said cavity resonator and the adjacent broad wall of said waveguide, and a second electron beam channeling tube being concentric with said resonator, said first electron beam channeling tube and said sleeve, said second beam channeling tube being rigidly afiixed through an electrically conductive connection to the remote wall of said waveguide and extending through said waveguide and sleeve into said resonator at said first end, said second beam channeling tube being spaced axially from said first beam channeling tube by a gap having a relatively fixed dimension; an electron gun for projecting an electron beam through one of said electron beam channeling tubes, across said gap and into the other of said beam channeling tubes; electron collector means connected to said other beam channeling tube; and means for tuning said cavity resonator while maintaining fixed the internal volume of said cavity resonator and the relative position of said first and second beam channeling tubes.

2. The velocity modulated vacuum tube defined in claim 1 which further includes an input cavity resonator intercoupling said first electron beam channeling tube and said electron gun, and means for electrically exciting said input resonator to velocity modulate the electrons emitted by said electron gun, said electrons being projected through said first tube into said second beam channeling tube.

3. The velocity modulated vacuum tube defined in claim 1 which further includes an input cavity resonator intercoupling said second electron beam channeling tube and said electron gun, and means for electrically exciting said input resonator to velocity modulate the electrons emitted by said electron gun, said electrons being projected through said second beam channeling tube into said first beam channeling tube.

4. A tunable multi-cavity klystron amplifier comprising: an input cavity resonator and an output cavity resonator concentric therewith, each of said cavity resonators having first and second apertured ends; a first electron beam channeling tube concentric with said cavity resonators and intercoupling said second end of said input cavity resonator with said first end of said output resonator; a second electron beam channeling tube coupled to said second end of said output cavity resonator; electron gun means coupled to said first end of said input cavity resonator for projecting a stream of electrons through said input cavity resonator, said first beam chan- 8 neling tube, said output cavity resonator, and into said second beam channeling tube; electron collector means connected to said second channel tube for absorbing electrons projected thereinto; a rectangular waveguide posi tioned adjacent one end of said output resonatorwith its broad walls normal to the axis of said resonators, the broad Wall of said waveguide nearest .said output cavity resonator having an aperture concentric with said cavity resonator; means forming a circular communicat-- ing passage between the aperture in said waveguide and the aperture in said one end of said output cavity resonator, the electron beam channeling tube coupled to said one end of said output resonator being rigidly connected to the .broad wall of said waveguide remote from said output resonator through an electrically conductive connection and extending through said Waveguide and said communicating passage into said one end of said output cavity resonator to provide a coaxialoutput link for extracting electrical energy from said output resonator; and means for tuning said cavity resonator while maintaining fixed the internal volume of said cavity resonator and the relative position of said first and second beam channeling tubes.

5. The klystron amplifier defined in claim 4 wherein said one end of said output resonator is said first end.

6. The klyst'ron amplifier defined in claim 4 wherein said one end of said output resonator is said second end.

7. A reflex klystron comprising: a cavity resonator having first and second apertured ends and an axis extending therethrough: electron repeller means connected to said second end of said resonator: a rectangular waveguide positioned adjacent said first end of said resonator, the broad walls of said waveguide being perpendicular to the axis of said cavity: means forming a communicating opening between the aperture in said first end of said cavity resonator and the interior of said rectangular waveguide; and electron gun means concentric with said cavity resonator and extending through said Waveguide and said communicating opening into said first end of said cavity resonator, said electron gun means being spaced from the sides of said communicating opening to thereby provide a coaxial link for propagating output energy from said cavity to said waveguide.

8. The klystron defined in claim. 7 wherein said electron gun means forms a door knob junction in said waveguide to provide a transition from said coaxial link to said waveguide.

9. In a tunable klystron vacuum tube, the combination comprising: a cavity resonator having an axis and first and second apertured ends; a rectangular waveguide positioned adjacent said first end of said resonator with its broad walls perpendicular to the axis of said resonator; means forming a circular communicating passage concentric with said cavity resonator between said first apertured end of said resonator and the interior of said waveguide; energy conversion means positioned adjacent the broad wall of said waveguide remote from said resonator; an electron beam channeling tube concentric with said resonator for channeling electrons between said energy conversion means and said resonator, said beam channeh' ing tube being rigidly affixed to said remote Wall of said waveguide through an electrically conductive connection and extending from said energy conversion means, through said waveguide and communicating passage and into said first end of said resonator, the diameter of said beam channeling tube being smaller than the internal diameter of said communicating passage to provide a coaxial link between said resonator and said waveguide; and means for tuning said cavity resonator While maintaining fixed the internal volume of said resonator and the relative position of said beam channeling tube and said resonator.

10. The klystron defined in claim 9 wherein said energy conversion means comprises an electron collector and wherein said klyst-ron further includes a second electron beam channeling tube afiixed to and extending into 9 10 said second end of said resonator, said beam channeling References Cited in the file of this patent lt ggggagerlng separated by a fixed dlstance w1th1n sa1d UNITED STATES PATENTS 11. The klystron defined in claim 9 wherein said en- 2,651,738 Ebers Sept. 8, 1953 ergy conversion means is an electron gun of a reflex 5 2,807,745 Moll Sept. 24, 1957 klystron. 

